This invention relates to a method of fairly controlling the excess usage of a finite resource, for example the usage of available bandwidth by permanent virtual circuits in frame relay networks.
In frame relay networks, permanent virtual circuits are set up through the network and frames are routed at each node in accordance with a virtual circuit id carried in the packet header. Available bandwidth is of course determined by the physical links and as a result congestion can occur in the network. When this happens frame relay may discard packets, which then must be retransmitted.
Existing frame relay networks (based upon current frame relay standards) have a problem with regards to the way in which spare/free bandwidth is allocated. Virtual circuits competing for excess bandwidth are not subject to fairness. Frames received by the switching mechanism are switched out to an outgoing transmit queue. If the transmit queue is congested (i.e. virtual circuits on that piece of bandwidth are transmitting more than the resource can handle) then the number of frames in the transmit queue will increase, potentially eventually overflowing. Essentially, the virtual circuit transmitting the most frames will get to consume the most bandwidth and the most transmit and buffering resources.
Current technologies, for example, as illustrated in the paper by D. B. Grossman entitled "An Overview of Frame Relay communications", CONFERENCE ON COMPUTERS AND COMMUNICATIONS, March 1991, and the paper by K. S. R. Mohan "Enterprise Networking using Frame Relay", PACIFIC TELECOMMUNICATIONS CONFERENCE, vol. 1, January 1993, in this area rely upon the Committed Information Rate and congestion procedures defined in the ANSI specifications. These procedures allow the user devices in a network to be policed to a committed information Rate (CIR), but burst up to an excess information rate (EIR). Excess burst traffic is marked as excess in frame relay by setting a DE (discard eligible) bit. DE frames are discarded in preference to non DE frames.
Other situations arise where the `excess` usage of any resource by competing users needs to be controlled.
An object of the invention is to provide a method of fairly controlling the excess usage of a finite resource.